1. Field of the Invention
The present invention relates to infusion apparatus and more particularly to an infusion system having a self-generating pressure assembly.
2. DESCRIPTION OF THE PRIOR ART
The prior art related to the infusion of blood, plasma or other fluids into the blood stream includes conventional infusion systems in which a container containing the fluid is elevated, usually several feet above the patient, to permit the force of gravity to overcome the intravenous pressure. In order to avoid the inconveniences and other disadvantages of elevating the container, several techniques have been employed including the use of mechanical pumping equipment and manual manipulation of a soft plastic envelope containing the fluid to be infused. For example, U.S. Pats. Nos. 2,766,907 and 3,153,414 show pressure infusion apparatus in which an inflatable bladder is connected to an external source of pressure such as a gas tank or squeeze bulb. The use of mechanical pumping means, pressure tanks or other external pressure equipment requires a source of power and the procurement, maintenance and storage of a substantial quantity of mechanical equipment for use on a mass basis. Manual manipulation of a soft fluid container is objectionable on a mass basis because it requires the extensive use of medical or para-medical personnel. Another and even more serious objection to the use of these techniques is that extreme caution must be excercised when using these techniques in order to prevent the introduction of air into the patient's veins, causing an embolism.
Some but not all of the disadvantages of the prior art have been overcome by the device shown in my U.S. Pat. No. 3,023,750 entitled "Self-Generating Pressure Device for Infusion Administration Systems". The device shown therein comprises a flexible container which stores a supply of fluid to be fed intravenously, and a sealed flexible bag folded within the container. The flexible bag contains a supply of a dry chemical in powder form and a liquid chemical contained in a frangible capsule. In use, the frangible capsule is broken by manipulation of the flexible container and the two chemicals mix and react generating a gas which expands within the flexible bag. The flexible bag unfolds and exerts pressure on the fluid stored within the flexible container, forcing the fluid to flow through an injection system which has a length of tubing communicating with the flexible container and with an injection needle.
Although this device eliminates the need for elevating the fluid container to overcome the intravenous pressure, there remains a small but nevertheless significant danger of an embolus being created when the fluid is exhausted, or nearly exhausted, from the flexible container and the expanding flexible bag continues to exert a force which may pump air into the injection system. In addition, since the expanding flexible bag is located within the fluid container directly in contact with the fluid, any leakage of gas from the bag would contaminate the fluid and endanger the patient.